CA1274504A - Method for rosin esterification - Google Patents

Abstract

Case Docket No. CHR 85-20 IMPROVED METHOD FOR ROSIN ESTERIFICATION

Abstract of the Invention The catalytic combination of phosphinic acid (also called hypophosphorous acid) and a phenol sulfide compound is disclosed to accelerate the reaction rate of esterification of rosin with a polyhydric alcohol, as well as provide product color improvements. According to the process of the invention, a rosin is reacted with up to a 50% equivalent excess of the polyhydric alcohol in the presence of phosphinic acid and a phenol sulfide compound at a temperature of from about 180°C to about 300°C.

Description

This invention relates to an improved method of preparing esters of rosin.
Rosln is mainly a mixture of C20, fused-ring, monocarboxylic acids, typified by levopimaric and abietiG
acids, both of which are susceptible to numerous ~hemi~al transformations. The rosins to which this invention relates include gum rosin, wood rosin, and tall oil rosin or the rosin acids contained therein as for example, abietic acid, pimaric acid, sapinic acid, etc.
The natural separation and gradual conversion of some of the hydrophilic components of sap and related plant fluids from the cambium layer of a tree into increasingly hydrophobic solids are the generic process of forming diverse gums, resins and waxes. The oleoresin intermediate in this proce6s i~ typified in pin gum, whiGh flows~from hacks on the trunks of southern yellow pine in southeastern Vnited States, in France, and in other countries. Pine gum contains about ~OX ~gum) rosin and about 20X turpentine.
Resinification from oleoresin can result from elther natural evaporation of oll from an extrudate or low collection in duct~ in sapwood and heartwood. Pinus stumps are valuable enough to be harvested, chipped, and extracted with hexane or higher-boiling paraffins to yield wood rosin, wood turpentine, and other terpene-related compounds by fractional distillation. In the kraft, i.e., sulfate, pulping process for making paper, pinewood is d1gested w1th alkali producing crude tall oil and crude ulf~ate turpentine as ~y-products. Fractionation of the crude tall oil yields tall oil rosin and fatty acids.
The chemlcal transformation of gum, wood, and tall~ oil resin which relates to this invention is èoterification. The ~eneficial product characteristics provided by ro~in esterification for various applications have led to the development of many esterification rQcedures~ particularly treatments with polyhydriG
alcohols. U.S. Patents 2,~6~,125, 2,5~0,~10 and 2,572,0 t~ch ro6in ecterification with glycerol and : ~ , -.. ,.. - .: , : -~2745~4 pentaerythritol, among other polyhydric alcohols, usually preceded by a rosin disproportionation step.
U.S. Patent 3,780,012 teache~ pretreating tall oil rosin with paraformaldehyde followed by di~tlllation prior to the esterification reaction to achieve product color improvement. U.S. Patent 3,~80,013 teaches the incremental addition of a phenol sulfide compound during tall oil rosin pentaerythritol esterification. The color of the product of these procedures was claimed to be an M
on the V.S.D.A. scale. The rosin color standards referred to in this invention are U.S.D.A. standards varying from X, the lighte~t, to D, the darkest color. The scale of colors i~ de~ignated as X, WW, WG, N, M, K, I, H, G, F, E, and D. Also, due to the light color of the rosin ester prvducts of the invention process, among X color rosins, the designations of X-A, X-B and X-C indicate lighter than X color, with X-C being the lighter color.
U.S. Patent 4,1~2,070 teaches employing arylsulfonic acid in place of the traditional basic esterification catalysts, such as calcium oxide, to reduce the time for tall oil ro~in-pentaerythritol esterification to obtain a rosin ester of improved oxygen stability, color and melting point. This work is confounded, however, by the unusually large amount of pentaerythritol used (35% equivalent excess) which by itself would markedly increase the rate of acid number drop. Products with Ring and Ball melting points of 77C to 86.5C were obtained. Normal commercial pentaerythritol esters of rosins have Ring and Ball melting between ~5C and 105C.
The ob~ect of this invention is to provide a novel method of preparing esters of rosin. It is a further ob~ect of this invention to employ a catalyst which accelerates the rosin esterification reaction rate to result ln a reduced reaction time. It is a still further ob~ect of this invention to permit a reduction in the amount of polyhydric alcohol employed in the reaction, resulting in reduced cost and higher, more desirable melting points, i.e., from ~5C to 105C. It is a ~2~4~;0~

specific o~ect of this invention to provide a method of preparing esters of rosin e~hibiting a color e~uivalent to or lighter than the starting rosin.
All of the above objects are met by the di~covery that phosphinic acid ~also called hypophosphorous acid) reacts synergistically with a phenol sulfide compound as a combined catalyst to accelerate the rosin esterification reaction rate.
Accordingly, the invention provides a process for esterifying rosin with a polyhydric alcohol which comprises heating the rosin and polyhydric alcohol in the presence of a catalytic amount of phosphinic acid and a phenol sulfide compound in an inert environment.
Thus, the improvement of this invention lies in reacting rosin and a polyhydric alcohol in the presence of phosphinic acid (H3Po2) and a phenol sulfide compound, as combined catalyst, to reduce the reacticn time for rosin pentaerythritol ester formation and to provide a rosin ester of improved color and oxidation stability.
Preferably, a rosin is reacted wlth at least an equivalent amount of a polyhydric alcohol, preferably glycerol or pentaerythritol, in the presence of from 0.1%
to 2.0% phosphinic acid and 0.05% to 1.0% of a phenol sulfide, based on the weight of the rosin, at a temperature of from about 180C to about 300C to produce a rosin ester having a color equivalent to or lighter than the starting rosin.
Phosphinic acid is a strong, reducing acid, useful for its antioxidant or color-reducing properties in the preparation of light colored fatty acid taurates (U.S.
Patent 3,232,968), carboxylic acid esters with poly~oxyalkylene) compounds (British Patent 979,673) and U.S. Patent 3,071,604), acrylic and methacrylic esters of glycols ~Japanese Patent 73 11084), or in light colored alkyl resins (Japanese Patent 12997). Also, phosphinic acld has been used as a tall oil treatment agent to convert the impurities and color bodies contained therein ,~

12~4504 to a non-distillable form and to promote decarboxyl~tion or rosin acids present ~u.s. Patent 2,441,197).
A novel rosin esterifiGation process is now provided involving the use of phosphinic acid in combination with a phenol sulfide compound as the esterification catalyst.
The gum, wood, and tall oil rosin materials to which this invention relates may be subjected to other treatments prior to esterification. For example, in addition to the distillation treatment alluded to in the fractionation extraction processes, the rosin material may have been sub~ected to disproportionation, hydrogenation, or polymerization, or some combination of these and/or other treatments.
As polyhydric alcohols, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, glycerol, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, mannitol, sorbital, as well as combination~ of the aforementioned and other similar polyhydric alcohols may be used. The amount of the alcohol used in the esterification may be varied widely but generally no more than an approximate 20%
exce~s over the equivalent combining proportion will be necessary.
In general, the esterification is effected by introducing the rosin, up to 50% eguivalent excess of a polyhydric alcohol, preferably 15-20% eguivalent exce~s, .. . .

~27~504 and from 0.1% to 2.0% phosphiniç acid, and from 0.05% to 1.0% phenol sulfide based on the weight of the rosin, into a reaction vessel. The reaGtion temperature is raised to from about 180C to about 300C, preferably from about 250C to about 280C, for up to about 15 hours of until the rosin acid number ls reduced to about 15 or helow.
Longer reaction times may be employed, but the additional time and energy costs generally outweigh any benefits received. The preferred amount of phosphinic acid is from about 0.2% to about 0.5%, based on the weight of the.
rosin, and no benefit i~ seen to be derived in employing amount~ of 0.5% or more of the phosphinic acid. The preferred amount of phenol sulfide i8 from about 0.2% to about 0.5%, based on the weight of the rosin.
The phenol sulfide is set forth in ~.8. Patent 3,~80,013. As stated ''~

~27~5{~4 Case Docket No. C~IR 85-20 in the aorementioned patent, the tr~ating agent may be represented by the structure: ¦
.i . I
(Hl)n ~(HI)n _ (lH)n (Aryl) -_ sx- ~ Aryl)sx ~ Aryl) (R)m (R)m --p (R)m '~here n is an integer from 1 to 3 inclusive, p is an integer from 0 to 100 and preferably about 5 to 20 inclusive, and the sum of m ,and n on each aryl is between 1 and 5 inclusive, x is 1, 2, or 3, and R is a hydrocarbon group, e.g., alkyl cycloalkyl and substituted alkyl, e.g., Cl-C8, wherein the substituents are ,cycloalkyl, aryl, alkaryl, and the like. R desirably contains ., "
from 1 to 22 carbon atoms inclusive~ Preferred alkyl groups are st-aight chain secondary and tertiary alkyl groups containing up to 8 carbon atoms inclusive. Preferred aryl groups are those containing 6 to 18 carbon atoms, inclusive, typically phenyl, naphthyl and anthracyl. Typical cycloalkyl groups con~ain 3-~carbon atoms in the ring, e.g., cyclopropyl, cyclopentyl and ~cyclohexyl.
!' Advantageously, the esteriiication reaction should be accomplished in the presence of an inert atmosphere, provided by 'a n trogen purge on the reaction vessel prior to addition of the reactants and a nitrogen sparge during the reaction. Since light color is ~ desirable property of the rosin ester and the color is sensitive to oxygen exposure, such exposure must be minimized.
Also, since an a~vancnge of the comblned phosphinic acid and phenol sulfide catalyst is minimal color degradation ,during esterification, the rosin ester color is primarily Il ~

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.. ... .. .. . .. .... ...

i27450A

Case Docket No. C~R 85-20 ,dependent upon the color of the starting rosin. When rosin is esterified, the combined catalysts of the invention process permit production of an ester~of an equivalent or lighter color jthan the starting rosin.
'1 In a preferred embodiment of the invention process, the ,;rosin starting material is melted in an inert atmosphere in the 1Ireaction vessel, followed by the addition of 0.2~ (based on the ;~weight of the rosin) of phosphinic acid (50% active in water), 0.5% (based on the weight of the rosln) of a phenol sulfide, and ¦15-20% equivalent excess pentaerythritol. A very low inert gas sparge, such as nitrogen or carbon dioxide, is maintained as the ~mixture is heated to 250C with agitation, which temperature is 'maintained for about three hours. The reaction temperature then ',is increased to 275C until the reaction product acid number is ' i, decreased to 15 or below, or for a time of about 2 to 12 hours.
iAfter about 5 to l5 hours from initiating the reaction, the inert ga~ sparge is replaced with a steam sparge, followed by addition - of about 0.053% solid sodium hydroxide (or other basic compound), ba6ed on the weight of the rosin, to neutralize the phosphinic acid catalyst, and the mixture is cooled to 220-230C and 1sparged with nitrogen to remove all moisture. (Alternatively, a '~50% a~ueous sodium hydroxide solution may be used.) ;1, The following examples serve to illustrate the unexpected color improvement in rosin estcrs made by the invention process, as well as the reduced reaction time. Unless "otherwise speciied, the parts are by weight. ~;

!~ Example l 1 In a suitable reaction vessel 500 parts of a tall oil ~ -- 'rosin with a U.S.D.A. color of WW was melted at 200C with a : !

'I 7 : -.. . .

Case Docket No. CHR 84-20 : nitrogen blanket. Pentaerythritol in the amount of 65 parts was added slowly at 200C. This mixture was heated to 250C for . i.
three hours with agitation, after which the temperature was increased to 275C and held until the reaction product acid number was 15. The total reaction time was 43 hours and the final ester had a U. S.D.A. color of I.
''~
' Example 2 j This and the following example show the benefits from employing a traditional rosin esterification catalyst in the reaction. The reaction was carried out as in Example 1 except, I
prior to the pentaerythritol addition, 1.076 parts of calcium ,formate were added as catalyst at 200C. The reaction time at !275C required to achieve a reaction product acid number of 15 ,was only 6-1/2 hours for a total reaction time of 9-1/2 hours.
;Also, the final ester had a U.S.D.A. color from M to K and a Ring aI~d Ball melting point of 100C.

E~ample 3 The reaction was carried out as in Example 2 except ,,1 part of calcium hydroxide was added as catalyst in place of 'calcium formate. The total reaction time required to achieve an acid number of 15 was 10 hours. The final es~er had a U.S.D.A.
- ~'color of ~, " Thus, the catalysts of Examples 2 and 3 provide reduced reaction time, but no real benefits in product color are achieved.
.;, ,1 ~ .

: ' "
.,, ,~ i . - ' -i274504 1 ~
~.
Case Docket No. CHR 85-20 Example 4 1 ';
To determine the benefits received from employing an arylsulfonic acid as a catalyst for the rosin esterification (as ¦ ' taught by U. S. Patent 4,172,070), the reaction was carried out j '~
' ,as in Example 1 except that after the pentaerythritol was added to the melted rosin and mixed well at 200C, 1 part of I , iparatoluenesulfonic acid was added. The time required to achieve ,an acid number of 15 or less was twelve hours. The final es~er ,, !l . .
had a U.S.D.A.,color of WW to WG. IJhile the reaction time was reduced over no catalyst and product color was better than that .' provided with the catalysts of Examples 2 and 3, little or no ¦
,,color reduction (lightening) from the starting rosin was noted. ¦ ,~
!
l :
~I Example 5 I, F`~
jl To determine whether an advantage is achieved by a ,'catalyst combination of an arylsulfonic acid and a phenol F' 'isul~ide, the reaction was carried out as in Example 4 except, ', ,after addition of the paratoluenesulfonic acid, phenol sulfide ' (Vultac@~ 2, an amyl phenol sulfide polymer sold by Pennwalt) was li ''added incrementally in amounts of 0.5 parts each at the beginning of the reaction, four hours later at 275C and, finally, four hours later at 275C. The total reaction time required to achieve an acid number below 15 was 10 hours, and the final ester jhad a U.S.D.A. color of X to WW. Thus, no significant ''improvement was noted over either of the catalysts used alone.
.1 , , E~ample 6 To show the synergistic catalytic and product color 1' ,improvement effect of the combination of phenol sulfide and "phosphinic acid in rosin esterification, the reaction was carried Il I
r~ . ....

,'" . ", ' ' -S,OA I ' ' ~;
Case Docket No. CHR 85-20 1 ;'' out as in Example 5 except, in place of the paratoluenesulfonic ¦ ' acid, 1 part of 50Z active phosphinic acid was added. Also, !
rather than incremental addition, all the phenol sulfide ! ~;
(1.5 parts) was added with the other reactants at the beginning of the reaction. After reaction for three hours at 250C, the 'temperature was increased to 275C for four hours to produce a 'final ester having an acid number below 13 and a U.S.D.A. color , of X-B to X-C.
I! i i ! ~
Example 7 i To show the benefit of the invention process for gum ~'ro3in esterification, the reaci~ion was carried O-lt as in - Example 6 except that gum rosin with a U.S.D.A. color of WG was ;.
employed as the starting rosin material. The final ester had an 1 ' acid number of 11 and a U.S.D.~. color of X-A to X-B.
,' Clearly, ~he marke~ improvement in the reaction time ' 'required to achieve the desired product acid number and the marked improvement (i.e., lightening) of product color using the catalyst combination of this invention exhibit an unexpected and unobvious synergistic catalytic effect for rosin esterification.

~'~ . While the invention has been described and illustrated 'herein by references to various specific materials, procedures 'and examples, it i8 understood that the invention is not 'reEitricted to the particular m~terials, combinations of 'materials~ and procedures selected for tha~ p~lrpose. ~umerous !l !
variations of such detail~i can ~e cmployed, as ~7ill ~e appreclated by those slcilled ~n the art.
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~ $ ~ r~
.~ 10 :

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for esterifying rosin with polyhydric alcohol which comprises heating the rosin and polyhydric alcohol in the presence of a catalytic amount of phosphinic acid and a phenol sulfide compound in an inert environment.

2. The process of claim 1, wherein the reaction is conducted in an inert environment for from 5 to 15 hours at from 180°C to 300°C in the presence of 0.1% to 2.0% phosphinic acid and 0.05% to 1.0% of a phenol sulfide compound, followed by a steam sparge and addition of a basic compound in an amount sufficient to neutralize the phosphinic acid.

3. The process of claim 1, wherein the rosin is esterified with up to 50% excess equivalent of the polyhydric alcohol at from 250°C to 280°C.

4. The process of claim 1, 2 or 3, wherein the rosin is selected from the group consisting of tall oil rosin, gum rosin and wood rosin.

5. The process of claim 1, wherein the rosin esterification i~ preceded by a rosin pretreatment step.

6. The process of claim 5, wherein the pretreatment step is selected from the group consisting of disproportionation hydrogenation and polymerization.

7. The process of claim 1, 2 or 3, wherein the polyhydric alcohol is pentaerythritol in an amount of 15-20% equivalent excess.

8. In a process for esterifying rosin with a polyhydric alcohol to obtain the corresponding ester, the improvement which comprises conducting the esterification reaction in an inert environment in the presence of from 0.1% to 2.0% phosphinic acid and from 0.05% to 1.0% of a phenol sulfide compound, based on the weight of the rosin, at a temperature of from about 180°C to about 300°c for a time required to achieve an ester product acid number of 15 or below and neutralizing the phosphinic acid.

The process of claim 8, wherein the rosin is esterified with up to 50% excess equivalent of pentaerythritol in the presence of from 0.2% to 0.5%
phosphinic acid and 0.2% to 0.5% of a phenol sulfide compound and the reaction is conducted under an inert gas sparge.

10. The process of claim 8, wherein the esterification reaction is conducted at a temperature of from 260°C to 280°C.

11. The process of claim 9, wherein the inert gas is selected from the group consisting of carbon dioxide and nitrogen.

12. The process of claim 8, 9 or 10, wherein the rosin is selected from the group consisting of tall oil rosin, gum rosin, and wood rosin.

13. The process of claim 8, wherein the rosin esterification is preceded by a rosin pretreatment step.

14. The process of claim 13, wherein the pretreatment step is selected from the group consisting of disproportionation hydrogenation and polymerization.

Case Docket No. CHR 85-20

15. The process of claim 8, 9, or 10 wherein the polyhydric alcohol is pentaerythritol in an amount of 15-20%
equivalent excess.

16. In a process for effecting rosin esterification which comprises reacting rosin with up to 50% equivalent excess of a polyhydric alcohol, based on the equivalent weight of the rosin, at a temperature ranging from 180°C to 300°C, the improvement of reacting the rosin and polyhydric alcohol for a time required to achieve an ester product acid number of 15 or below in tlle presence of from 0.1% to 2.0% phosphinic acid and from 0.05% to 1.0% of a phenol sulfide compound of the structure:

where n is an integer from 1 to 3, p is an integer from 0 to 100, x is 1 to 3, the sum of m and n on each aryl is from 1 to 5, aryl is selected from the group consisting of phenyl, naphthyl, and anthracyl, and R is a hydrocarbon radical of 1 to 22 carbon atoms.

17. The process of claim 16 wherein the rosin is selected from the group consisting of tall oil rosin, gum rosin, and wood rosin.

18. The process of claim 16 wherein the polyhydric alcohol is pentaerythritol in an amount of 15-20% excess equivalent.

Case Docket No. CHR 85-20

19. The process of claim 16, 17, or 18 wherein the time required to achieve an ester product acid number of 15 or below is from 5 to 15 hours.